Gas-Phase Hydrodeoxygenation of Benzaldehyde, Benzyl Alcohol, Phenyl Acetate, and Anisole over Precious Metal Catalysts

The aim of this work is to study the gas-phase hydrodeoxygenation (HDO) of bio-oil-related platform molecules over precious metal catalysts (Pt and Pd on alumina) at moderate temperature (325 degrees C) and low pressure (0.5 MPa). Bio-oils consist of a complex mixture of compounds, many of which are aromatic oxygenates, and have been modeled here by four model compounds with different oxygenated functional groups: benzaldehyde (aldehyde), benzyl alcohol (alcohol), phenyl acetate (ester), and anisole (ether). First, the stability and activity of the catalysts in the HDO of the different compounds have been studied in an isothermal fixed-bed reactor. The performance of the Pt catalyst is better than that of the corresponding Pd catalyst (highest activity and selectivity). The compound more refractory to HDO over Pt was benzyl alcohol. Both catalysts suffer from strong deactivation at the beginning of the tests, mainly by the formation of carbonaceous deposits. The deactivation is particularly strong for the HDO of benzyl alcohol over the Pd catalyst. Second, a kinetic study has been carried out varying the space time (0-1 (kg(cat) s)/mol). Kinetic models, based on reaction networks derived from the product distributions, have been proposed, and the kinetic constant fit to the experimental data by least-squares regression.